Do you need to know how something works just to use it?
No, but it does help when you have to explain how you haved fixed something.
Sometimes.
I fixed a TV set for a friend that had just a loose wire needing to be resoldered, but when I tried to explain what I had done I might as well have been telling him that I had used my mad witch doctor skillz to scare away the evil spirits that were preventing this TV from working. The guy was perfectly satisfied with not knowing how his TV worked as long as he could operate it and watch the shows he wanted. I think the vast majority of technology users are like that.
With mechanics and electronics, I'm a good common sense technician - but everything I know is pretty much self-taught so there are points of supurb insight coupled with bizarre gaps in knowledge.